Cellular damage to lipids, proteins, and nucleic acids by endogenously generated peroxynitrite is associated with a number of neurological diseases. Results of earlier studies in this laboratory demonstrated that the ability of peroxynitrite to damage proteins is strongly dependent upon the hydrogen ion concentration and physiological levels of carbon dioxide and that it probably does not contribute significantly to formation of protein carbonyl derivatives or to the oxidation of methionine residues, both of which are widely used markers of oxidative protein damage. In continuing studies to identify major targets for peroxynitrite-dependent modification of proteins, the ability of peroxynitrite to nitrate tyrosine residues in bovine serum albumin (BSA) and glutamine synthetase (GS) was determined. Although these two proteins contain nearly identical numbers of tyrosine residues per subunit, they exhibit markedly different pH-dependent profiles of peroxynitrite-dependent nitration. It is thus evident that nitration of protein tyrosine residues is strongly dependent upon the molecular distribution of tyrosine residues and protein conformation. - peroxynitrite, protein carbonyls, peroxynitrite-carbon dioxide adducts